Add support for Date/Time attribute values (#903)

Closes #883

Author: joeldrapper

lib/phlex/sgml.rb

@@ -481,6 +481,10 @@ def json_escape(string)
 				v.name.tr("_", "-").gsub('"', """)
 			when Integer, Float
 				v.to_s
+			when Date
+				v.iso8601
+			when Time
+				v.respond_to?(:iso8601) ? v.iso8601 : v.strftime("%Y-%m-%dT%H:%M:%S%:z")
 			when Hash
 				case k
 				when :style

quickdraw/sgml/attributes.test.rb

@@ -176,6 +176,16 @@
 	assert_equal_html output, %(<div attribute="1.234"></div>)
 end
 
+test "_, Date" do
+	output = phlex { div(attribute: Date.new(2023, 1, 15)) }
+	assert_equal_html output, %(<div attribute="2023-01-15"></div>)
+end
+
+test "_, Time" do
+	output = phlex { div(attribute: Time.new(2023, 1, 15, 12, 30, 45)) }
+	assert_equal_html output, %(<div attribute="2023-01-15T12:30:45+00:00"></div>)
+end
+
 test "_, *invalid*" do
 	assert_raises(Phlex::ArgumentError) do
 		phlex { div(attribute: Object.new) }